Ink-jet recording is carried out in such a manner that fine ink droplets are jetted onto a recording sheet such as a paper sheet, employing various working principles so that images and text are recorded. Said ink-jet recording exhibits advantages such as relatively high speed, low noise, and easy multicolor reproduction.
Conventional drawbacks with nozzle clogging and maintenance in said recording method have been overcome due to improvement of both inks and devices. As a result, at present, said recording method has been increasingly applied to various fields such as various types of printers, facsimile machines, and computer terminals.
Recently, said printers have been particularly improved so as to produce high quality images which approach conventional photographic image quality. Accordingly, needed are recording sheets capable of realizing conventional photographic quality and of further reproducing conventional photographic print-like properties (glossiness, smoothness and toughness).
As an example of the recording paper capable of forming such the high quality image, an ink-jet recording paper having a swelling type ink receiving layer is known. Such the recording paper gives a recorded image near a photographic image in the textile feeling thereof. On the other hand, the ink-jet recording system is developed so that the recording speed is raised. Accordingly, it is demanded that the recording paper has high ink absorption ability and a high drying speed. However, in the ink-jet recording paper having the swelling type ink receiving layer, the ink absorbing speed is low and a spot caused by combining of the ink droplets tends to be occurred in the recorded image when the image is formed by a high speed recording. Moreover, the recording paper has a drawback such that the ink tends to be spread when the printed image is stored under a high temperature condition.
To solve such the problems, an ink-jet recording paper improved in the ink absorbing speed and the anti-spreading ability is known, which has a porous ink receiving layer constituted by a little amount of a hydrophilic binder and a cross-linking agent, a large amount of a fine particle, hereinafter referred to as a filler fine particle, and a binder. The porous type ink receiving layer is classified into one mainly constituted by inorganic filler fine particles having an average particle diameter of approximately 1 μm and one mainly constituted by inorganic filler fine particles having an average particle diameter of 100 nm or less.
The recording paper using the inorganic filler fine particles having an average particle diameter of approximately 1 μm is insufficient in the smoothness of the surface and surface glossiness even though the ink absorbing speed is very high. Besides, in the recording paper using the inorganic filler fine particles having an average particle diameter of 100 nm or less, the ink absorbing speed is high and an image can be obtained, which has a highly smooth surface with a high glossiness and a textile feeling near that of the photograph.
However, the ink absorbing speed of the porous layer constituted by the inorganic filler fine particle having an average particle diameter of 100 nm or less is not always sufficient considering the raising of the recording speed in future. Consequently, further rising of the ink absorbing speed is demanded.
It is considerably effective for raising the ink absorbing speed to lower the content of the hydrophilic binder. In such the case, however, cracks in the coated layer are easily occurred in the course to the production since the adhering force between the filler fine particles is lowered. It is considered that the use of a binder with a low hydrophilicity or a hydrophobic binder is advantageous. However, such the layer is not suitable for the coating by an aqueous system and a problem on the environmental suitability is caused.
As a method for coating the hydrophobic binder by an aqueous system is known, by which the binder is added in a state of emulsion such as latex to an aqueous coating liquid. However, the ability for effectively binding the filler fine particles of the usually used binder emulsion is low since the average particle diameter of it is so large as from 200 nm to 1 μm and the surface area per weight is small. Such the tendency is made conspicuous when the filler fine particles having the average particle diameter of 100 nm or less are used.
On the other hand, in addition to said image quality and conventional-print like properties, higher level of durability as well as image retention properties has been demanded and much researches has been conducted to improve light fastness, moisture resistance, and water resistance to the level of silver halide photography. For example, regarding improvement of the light fastness, many techniques are disclosed in Japanese Patent Publication Open to Public Inspection Nos. 57-74192, 57-87989, 57-74193, 58-152072, 64-36479, 1-95091, 1-115677, 3-13376, 4-7189, 7-195824, 8-25796, 11-321090, 11-277893, 2000-37951.
In addition to the light fastness problem, porous type recording sheets have a problem in which, due to the multiple-void structure, discoloration and fading tend to occur due to harmful gases. Water-soluble phthalocyanine based dyes, which are employed in common color ink-jet printers, tend to result in said problem.
The mechanism of said discoloration and fading has not yet been fully clarified. However, it is assumed that a very small amount of active harmful gases such as ozone, oxidants, SOx, and NOx in ambient air decomposes said dyes, since the multiple-void structure has a large surface area and an active surface of inorganic fine particles.
Techniques for reducing said discoloration and fading are described in Japanese Patent Publication Open to Public Inspection Nos. 63-252780, 64-11877, 1-108083, 1-216881, 1-218882, 1-258980, 2-188287, 7-237348, 7-266689, 8-164664, and others. However, recording sheets for producing photographic image quality, utilizing a finer multiple-void structure than conventional, tend to be more readily degraded. Accordingly, conventional improvement techniques have not resulted in sufficient effects and more essential improvement has been demanded.
Said swelling type recording sheets tend to result in fewer such problems, but exhibit inherent difficulty to improve the low ink absorption rate.
It is possible to overcome discoloration and fading problems by utilizing an ink-jet recording method in which a pigment-based ink is used. However, drawbacks such as bronzing on the recording sheet surface have not been overcome so as to result in sufficiently acceptable image quality in terms of overall product quality. Further, the following gas insulation methods are very effective: prints are subjected to a lamination treatment or placed in a frame, or as described in Japanese Patent Publication Open to Public Inspection Nos.53-27426, 59-222381, 62-271781, 11-157207, 11-245507, and 2000-71608, recording sheets, comprising fine thermoplastic particles on the surface, are printed, and subsequently heated or pressed to result in formation of a gas insulation layer. However, each of said methods needs a post-treatment to result in an additional manufacturing process.